1. Field of the Invention
This invention relates to filling pressure vessels, particularly hybrid air bag inflators, with gas.
2. The Related Art
Present-day automotive vehicles incorporate one or more inflatable air bags for the protection of occupants in the event of a crash. The air bags are mounted in a folded compact condition in cooperative relation with a gas inflator. Upon sensing an impending vehicle crash, the inflator produces inflation gas which rapidly inflates and deploys the air bag.
Many types of inflators have been disclosed in the art for use in inflating air bags in such crash protection or safety restraint systems. One involves the utilization of a quantity of stored compressed inflation gas which is selectively released to inflate the air bag. Another derives a gas source from a combustible gas generating material which, upon ignition, generates a quantity of gas that is sufficient to inflate the air bag. In a third type, the air bag inflation gas results from a combination of stored compressed gas and gas generating material. The last mentioned type is commonly referred to as an augmented gas or hybrid inflator.
The compressed or pressurized supply of gas is a very important part of a hybrid inflator. The pressurized vessel typically is compressed or pressurized with an inert gas such as argon, or a mixture of argon and another inert gas, to approximately 3000 psi at room temperature. The invention, in general, is applicable to compressed gases. The phrase compressed gases is understood to encompass inert, flammable and non-flammable gases, either existing alone or in certain proportions. The limit of 3000 psi at room temperature is illustrative only and is not intended in any manner to place restrictions on the scope of the claimed invention.
A U.S. Department of Transportation (DOT) requirement on hybrid inflators calls for a proof pressure that exceeds the pressure of the contents at 130.degree. F., with a 30-second hold-time requirement. Current practice for proof testing hybrid inflators requires over-filling the inflator (at room temperature) to the desired proof pressure, then venting the extra gas until the desired fill pressure is reached.
An alternative being considered would separate the proof and fill stages, conducting them at different points on the production line. Both methods require significant time and wasted gases. Neither method proof-tests the ball weld that is used to seal the inflator.
There are two other methods that are commonly used when proof-testing pressure vessels. One method is to conduct the test with a liquid, such as water, as a step separated from the filling process. The other method is to fill and seal the vessel, and then heat the assembly to increase the pressure of the gas. Both methods are time consuming and require a separate production station for the proof test.
There is thus a need and demand for improvement in the techniques that are used when proof testing pressure vessels, and in particular, hybrid inflators in order to reduce the time required to carry out the proof testing process to avoid wasting of gases, and also to proof test the weld that is used to seal the inflator. The present invention was devised to fill the technological gap that has existed in the art in this respect.
A method of filling a pressure vessel with gas is disclosed in application Ser. No. 08/490,186 (Docket 2577-21-00) filed Jun. 14, 1995 in the United States Patent Office by Daniel R. Leininger and Walter A. Moore entitled "High Rate Pressure Vessel Filling Process" and assigned to the assignee of the present invention. A characteristic of this method is that the volume and temperature of the gas going into the vessel are controlled to ensure a consistent fill mass.
The present invention devises on the Leininger and Moore method by setting the controlled temperature high enough to cause the fill pressure to exceed the required proof pressure. The vessel can be sealed immediately after filling, and the pressure will decrease as the contents cool. If a required hold time is specified in connection with the proof test, the temperature can be set high enough to allow for cooling of the contents during the hold time. This method eliminates the need for a separate proof test step and greatly reduces cycle time.